Lecture series

Archive of presentations delivered to the ASR

A/Prof. Patrick T. Spicer (UNSW)

Microscale Yielding of Fibre Gels()

(A video of the presentation can be foundhereor under the video menu once logged in)

Complex fluids have been studied and developed in many sectors of industry and medicine because of their unique rheological properties. Suspending colloidal particles with attractive interactions to form a network is a common way to impart a yield stress to a fluid. Large aspect-ratio cellulose nanofibers are able to a form poroelastic network at low volume fractions via aggregation and entanglement, forming a gel without significantly modifying viscosity. Such nanofiber gels have a small, but useful, yield stress and a better ability to suspend particles than higher volume fraction glasses. In this study, an active microrheology technique is used to study deformation and yielding of weak cellulose fibre gels. Microrheology coupled with confocal imaging shows how gel yield stress can be a strong function of the structural deformation rate because of localized network restructuring. Such response is advantageous to numerous applications like surface coatings, nasal sprays, cosmetics, and foods. Understanding the mechanism of rate- and length-scale dependent yielding, and relating microstructure changes to bulk rheology, will enhance our ability to formulate, model, and design complex fluids with novel performance.

A/Prof. Chiara Neto (The University of Sydney, AINST)

(A video of the presentation can be foundhereor under the video menu once logged in)

The traditional assumption of a no-slip boundary condition at liquid–solid interfaces provides a good description of liquid flow on a macroscopic scale. However, on the microscopic scale a finite slip for simple liquids can be detected using high precision nano-scale techniques. The occurrence of interfacial slip is important in all situations where liquid flow is confined, such as in microfluidic and biological systems.

For the past few years my group has investigated the boundary conditions for flow by measuring hydrodynamic drainage forces using the colloid probe Atomic Force Microscope (AFM). We have been able to provide new experimental data, an improved analysis protocol, and a new theoretical approach which overall greatly enhance the accuracy and reproducibility of the measured slip.

The investigation of the flow of liquids in biological systems in particular requires the design of soft interfaces. Grafting polymer brushes is an ideal way to fabricate controlled soft interfaces, thanks to their versatile chemical functionality, and their switching of properties in reaction to stimuli. In this work the interfacial flow of a Newtonian liquid was investigated at the interface with densely grafted layers of polyethylene glycol, of two different chain lengths, obtained by grafting under marginal solvation conditions. The hydrodynamic force measurements confirm earlier molecular dynamics simulations that the slip length can be interpreted as a penetration length, which accounts for flow within the top half of the polymer brush.

05 April 2017

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RMIT University, Melbourne, Australia

Mr. Phred Petersen (RMIT)

Smoke and Mirrors: Flow visualisation just for the fun of it

This talk will be a visual tour of flow visualisation experiments that have been driven mostly by personal curiosity, and an interest in seeing the order of nature in ways that blur the boundaries between science and art.

Dr. Chris Garvey (ANSTO)

Getting statistical and structural in shear

Neutron scattering provides a non-destructive tool to probe materials undergoing shear, and a unique structural perspective on complex fluids and soft matter, probing length-scales up to microns. I will introduce the neutron scattering facilities at the Australian Centre for Neutron Scattering on ANSTO's Opal reactor, the range of sample environments available, and the possibilities for structural investigations on neutron scattering beamlines.

11 April 2016

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The University of Sydney, Sydney, Australia

Ms. Jasmine Pour (Duromer Products Pty. Ltd.)

Microstructure and Rheology of Reinforced Nylon 6 ()

(A video of the presentation can be foundhereor under the video menu once logged in)

Relationships between the rheological and mechanical properties of Nylon 6/Wollastonite were examined. The aim of this study was to determine the optimum twin-screw extruder operational conditions to achieve desired mechanical properties controlled by Microstructure. The results showed that the operational conditions had a strong influence on final properties of the composite, which were attributed to mineral features and aspect ratio before and after compounding and, also, the existence of hindered polymer chains and the physical co-continuous structure formed between particles. The observed low frequency liquid-like to solid-like transition and apparent yield stress in simple shear flows, along with nonzero values in stress relaxation after the cessation of flow experiments, were found to be consistent with formation of a physical network in quiescent conditions.

Dr. Pierre Rognon (School of Civil Engineering, The University of Sydney)

How rheology can help mitigating landslide and snow avalanche hazards ()

(A video of the presentation can be foundhereor under the video menu once logged in)

How does soil and snow flow? Answering this question is essential to predict landslide and snow avalanche pathways, and thus to mitigate these hazards effectively. This talk will introduce some key rheological properties of flowing soils and snow avalanches observed in field experiments, laboratory experiments and DEM simulations that I have been conducting over the last ten years. The discussion will focus on establishing constitutive models capable of capturing and predicting these properties, and on the crucial role played by the granular microstructure of these materials.

14 Jan 2016

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RMIT University, Melbourne, Australia

Prof. Gareth McKinley (Massachusetts Institute of Technology)

(A video of the presentation can be foundhereor under the video menu once logged in)

Many soft materials including foods, consumer products, biopolymer gels & associative polymer networks are characterized by multi-scale microstructures and exhibit power-law responses in canonical rheological experiments such as Small Amplitude Oscillatory Shear (SAOS) and creep. Even in the linear limit of small deformations it is difficult to describe the material response of such systems quantitatively within the classical framework of springs and dashpots – which give rise universally to Maxwell-Debye exponential responses. Instead empirical measures of quantities such as ‘firmness’, ‘tackiness’ etc. are often used to describe and compare material responses. G.W. Scott Blair argued that such measures are best thought of as ‘quasi-properties’ that capture a snapshot of the underlying dynamical processes in these complex materials. We show that the language of fractional calculus and the concept of a ‘spring-pot’ element provide a useful ontological framework that is especially well suited for modeling and quantifying the rheological response of power-law materials. We illustrate the general utility of this approach by describing fractional differential forms of the Maxwell and Kelvin-Voigt models and using these models we quantify small-amplitude oscillatory shear responses and creep response in range of soft materials including soft solid foodstuffs such as cheese, gluten and casein gels, skin and soft tissue, filled polymer melts, hydrogen-bonded biopolymer networks and the complex interfacial rheological properties of acacia gum and serum albumins. The fractional exponents that characterize the dynamic material response can also be connected directly with the scaling exponents from microstructural models such as the Rouse model and the Soft Glassy Rheology (SGR) model. Having determined the quasi-properties that quantify the linear viscoelastic material response of a power-law gel in a concise form, we show that a fractional K-BKZ framework combining a MittagLeffler relaxation kernel with a strain-damping function can be used to quantitatively describe the nonlinear viscometric properties of such materials. Depending on the range of values of the quasi-properties the resulting models can have some surprising features, including; agreement with wellknown heuristics such as the Cox-Merz rule and the complete absence of a zero-shear-rate plateau in the viscosity and the first normal stress difference.

22 Sep 2015

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The University of Melbourne, Melbourne, Australia

Dr. Daniel Lester (RMIT University)

Non-Newtonian materials such as granular matter, polymer melts, emulsions, suspensions and biological materials are typically considered "difficult" to mix, chiefly due to restrictions imposed by complex viscosity, shear sensitivity or energy consumption. Consideration of the physics of mixing from a dynamical systems perspective indicates that all materials which can be deformed in some way (e.g. via shear, stretching of slip) can admit rapid, complete mixing via judicious programming of these simple deformations. Compared with traditional approaches to mixing, such programmed deformations minimise energy consumption and imposed stress whilst significantly accelerating hat and mass transfer, often by several orders of magnitude. We present an overview of these applications from micro-fluidic to industrial scales, and consider a class of topological mixers which achieve efficient mixing of continua regardless of material rheology.

Dr. Peter Harbour (Eco Harvest)

The Study of Sludge Dewatering using Reebeds

Reedbeds have been used quite successfully for sludge drying and sludge dewatering in Europe since the late 1980s. They are relatively popular due to low operational complexity, low opex costs, low energy use and low maintenance requirements. Even though climatic conditions are far more favourable in Australia, adoption has been non-existent. Whilst the application of reedbed systems to sludge dewatering and drying is extremely simple, the processes behind these systems are quite complicated and understanding is limited. Peter will present the application of reedbeds to sludge drying for both sewage sludge and potable water sludge, an outline of the dewatering and drying processes involved and touch on some of the research done to gain a better understanding of these systems.

Microfluidic Extensional Rheology

Extensional flow is present in systems we see day to day, and others that have academic or wide ranging industrial applications. Understanding extensional properties of different fluids, particularly, non-Newtonian material can assist in improving system efficiencies and permit the utilization of beneficial phenomena. Failing to predict the extensional behaviour of non-Newtonian fluids can lead to frustrating fluid formation and application system design, or worse, widespread environmental damage. However, there are few tools available for performing rheological extensional flow analysis.

This is in contrast to the shear techniques, which have been around much longer. There are considerable technical difficulties involved in producing reliable extensional experiments and further difficulties in analysis. These challenges become exacerbated for low viscosity fluids due to the small time scales and dominance of inertial effects.

We present a novel microfluidic technique that has been developed to analyse fluids with water like viscosities which exceeds the range and capabilities of alternative technologies through its utilization of surface acoustic waves. We also discuss the novel fluids such as weekly elastic aqueous polymer solutions, Nano metal particle suspensions and swimming microorganism suspensions.

12 Nov 2014

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Monash University, Melbourne, Australia

Dr. Tapio Simula (Monash University)

Quantum turbulence

Superfluids are fluids which have the ability to support persistent currents and frictionless flows. Rotation in superfluids is possible through nucleation of vortices whose circulation is quantized. Turbulence in such fluids is coined quantum turbulence and corresponds to chaotic, topologically protected, dynamics of these whirlpools of the quantum world.

This presentation begins with an introduction to basic concepts of superfluidity and quantized vorticity. A brief outline of key concepts of turbulence, highlighting the differences and similarities between classical fluids and superfluids, are then presented. This is followed by a more detailed discussion of recent theoretical and experimental results in the emerging field of two-dimensional quantum turbulence. Questions are welcomed throughout the talk.

Dr. Russell Varley (CSIRO Manufacturing)

Making Composites that last longer, perform better and are more sustainable: It's always about the rheology!

The excellent strength to weight ratio and corrosion resistance of polymer composites makes them very attractive to industries that are developing more sustainable manufacturing processes and products. It is their reduced weight in particular however, that is driving wider usage in the aerospace, automotive and Oil and Gas industries, such that the new Boeing 787 and Airbus 350 now consist of about 50% polymer composite. While the promise of reduced weight underpins these applications, it is actually the developments in polymer processing and new processable resins systems that have enabled composites to take full advantage, through improved product quality, reliability and control. Clearly, understanding the interplay between the chemical and visco-elastic changes which occur during processing is critical to final properties and performance. As you would expect, it’s all about the rheology!

This presentation therefore, will introduce some important rheological and viscoelastic concepts, such as gelation, resin infusion, vitrification, crystallisation and glass transition temperature in the context of processing high performance polymer composites, both thermoplastic and thermosetting. Using examples from different areas of our polymer composite research, the importance of understanding and controlling rheological behaviour during processing and its impact upon properties and function will be discussed. This will include a brief introduction into novel high performance self-healing polymer composites, the challenges of ring opening polymerisation of thermoplastic polymers and the quest for the next generation high performance epoxy composites.

15 May 2014

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Edith Cowan University, Perth, Australia

Dr. Phillip Fawell (CSIRO)

The study of flocculation in mineral processing is complicated by the viscous nature of the aqueous solutions formed from high molecular weight acrylamide/acrylate copolymer flocculants. Comparisons of flocculant products suffer when physical mixing issues aren’t separated from “chemistry issues” associated with surfaces, adsorption and aggregate growth. In full-scale applications, excessively high flocculant concentrations can contribute to poor flocculation even in turbulent feedwells. This presentation will describe some results from a range of techniques that have been applied to better understand this problem, towards capturing such effects in computational fluid dynamics (CFD) modelling. This will include flocculation kinetics measurements, ultrasonic velocity profiling (UVP) and electrical resistance tomography (ERT). Recent progress in the AMIRA P266G “Improving Thickener Technology” project in CFD modeling of concentrated flocculant dosing into turbulent flow will be briefly discussed.

Dr. Alex Lubansky (Edith Cowan University)

Can microfluidic contractions be used as planar extensional rheometers? An analytical analysis

Measuring the extensional rheology of a fluid reliably, simply and cheaply has presented a long-standing challenge. While some techniques have recently gained popularity and acceptance for measuring the uniaxial extensional viscosity, such as CaBER or FISER, determining the planar extensional rheology has proven more challenging. Recent efforts have focused on using microfluidic contractions for testing, although there remains outstanding questions surrounding the appropriate analysis. In this presentation, I will discuss the importance and usefulness of extensional rheology measurements, and will highlight some of the important considerations that can take place when measuring extensional rheology of dilute and semi-dilute polymeric solutions.

13 November 2013

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Swinburne University of Technology, Melbourne, Australia

Prof. John Sader (University of Melbourne)

Fluid-Structure Interaction at Nanometre Scales

Miniaturisation of resonant mechanical sensors has led to unprecedented resolution, including the ability to image surfaces and measure mass at the atomic level. For applications in biology and environmental sensing, characterisation of the fluid-structure interaction of these smallscale devices is essential. In this presentation, I shall discuss recent work in my group aimed at modelling the fluid-structure interaction of nanometre-scale mechanical devices, in gas and liquid. This will include a comparison of the developed theories with measurements performed at the Argonne National Laboratory, California Institute of Technology and the University of Chicago.

Ms. Hui-En Teo (University of Melbourne)

Understanding the yield behaviour of suspensions under combined shear and compressive loads

Understanding the flow behaviour of particulate fluids is essential for optimising industrial suspension processing. To that end, suspension rheology research has resulted in the characterisation of yield behaviour through two key material properties: the shear and compressive yield stress, σy and py. These parameters give a viscoplastic description of yielding in concentrated suspensions above the gel point. As py is typically an order or two greater than σy, the effect of one on the other can be ignored in predominantly one-dimensional processes such as pipeline flow of non-settling suspensions and pressure leaf filtration. However, great difficulty is faced when attempting their application into multi-dimensional processes which are not properly understood rheologically. Such combined loading operations, like roll compression, raked thickening and belt filtration, occur in many industrial processes. As a first step towards modelling multi-dimensional processes, the constitutive behaviour of suspensions under combined shear and compression is sought. Individual requirements for the accurate determination of σy and py are the avoidance of wall slip in shear and the application of differential pressure in compression. Taking these into consideration, the experimental method employs an ARES rheometer loaded with a sintered disc and dead weights. Exploration of the effect of compression on material shear properties was conducted on a model inorganic calcite suspension. From controlled rate stress relaxation data, the shear modulus G(t) and strain softening function h(q) were extracted and compared. The sub-yield behaviour from constant rate tests was also fitted to a standard linear solid (SLS) model. It was observed that under the two types of rheometric testing, shearing under minor compression resulted in higher stress peaks and quicker stress dissipation than in the unloaded case. The development of transient force chains within the suspension is postulated to affect the stress behaviour of the sheared material. These findings point to significant interaction between shear and compressive loadings in suspensions.

16 May 2013

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RMIT University, Melbourne, Australia

Dr. Franco Costa (Autodesk)

Challenges in prediction of Injection Molding ()

Moldflow has been used to predict the injection molding process and final part shape for 35 years, but challenges still remain. An introduction to the analysis capabilities of the Moldflow software package and how rheology plays a part in this will be given. Following this introduction, there will be discussion of some of the current research areas and remaining challenges in understanding of polymer melt behavior. Topics will include crystalline morphology, long fiber composites, shrinkage prediction, thermal and fill pattern imbalances and incidences of slip behavior.

Dr. Predrag Micic (Qenos)

The Power of Collaboration — Commercialisation of a World First Polymer Technology

Polyethylene is widely used in the manufacture of pipes for pressure applications. On a global basis, the market for polyethylene in pipe applications is amongst the highest growth areas. This is particularly true in Australia, where the importance of water management, growth of the mining sector, and the development of coal seam gas projects, has created exceptionally strong demand for polyethylene (PE) pipes. The growing demand for PE pipes is driven by the benefits they offer in long term performance and ease of installation. Over the past 50 years the R&D activities of both universities and polyethylene technology companies has resulted in several generations of PE for pipe, leading to the current high performance PE100 resins. These advances have been achieved through enhanced understanding of structure-property-performance relationships, and the application of catalyst and process know-how to modify the molecular structure and deliver enhanced pipe performance. PE100 performance is achieved by leveraging the strength and processing balance possible from a bimodal molecular weight distribution. This is typically achieved by the use of dual reactor systems (Fig 1). The challenge for Qenos was to utilise existing single Unipol reactor asset (Fig 2) to produce a bimodal PE100 resin. Fig 1: Dual Slurry Reactor System. Fig 2: Single Unipol reactor system. Qenos is exceptionally strong in understanding market needs and translating them into polymer structure to deliver the required performance. However, the challenge facing Qenos required a break through catalyst technology, and was outside the scope of in-house R&D capability. Qenos called on its research partner, Univation, for the specific scientific input to develop a catalyst that could assist Qenos to create the required molecular architecture in a single Unipol gas phase reactor (Fig 2). The resultant collaboration has been an extraordinary success for both parties. This paper will describe the significant challenges encountered from initial concept through to commercialisation, along with the critical elements that made the collaboration successful. Qenos’ new PE100, HDF145B, is a world leading resin allowing new applications for polyethylene pipes. Our customers have been able to produce pipes up to 2 metres in diameter, and with wall thickness up to 110 mm. These are dimensions not previously possible with existing resins. Qenos is manufacturing tens of thousands of tonnes of PE100 using this technology each year, and Univation is licensing the catalyst technology to a global client base. This is truly a win–win outcome for both the industrial partner and the research provider, and of significant benefit to Australian industry.

03 April 2013

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University of Western Australia, Perth, Australia

Dr. Milan Patel (CSIRO)

Flour quality and dough sheetability ()

Conventional dough rheology tests, as practiced in the cereal industry for assessing end use applications of wheat, are performed with doughs that are mixed to optimal water absorption set at 500 BU in a Farinograph mixer. Dough consistency corresponding to 500 BU is considered acceptable for handling and the rheology tests are used to further delineate between flours for end use applications - breads, cakes, feed etc. In addition, flours that require a higher proportion of water to form 500BU doughs are more profitable for product manufacturers. As a result, lower protein flours, which require less water to form optimal doughs, are discarded immediately for bread making applications. However, this paradigm changes when the method for dough processing is sheeting, in which wetter, low protein doughs can be handled. High quality breads have been made from these flours. The question becomes how to characterise flours for dough sheetability. Chakrabarti-Bell et al. [1] showed that dough’s elasticity dominates dough behaviour during sheeting by incorporating a rheological model for dough into finite element simulation of sheeting. Therefore, to develop a method for characterising dough sheetability, a project was carried out using six different flours sourced around the world, varying in both protein content and water absorption. Each flour was mixed at three different flour-water ratios and then sheeted using an instrumented single roll sheeter. True rheological properties were also measured and the data fitted to a modified Bergstrom-Boyce model for dough [1]. Good agreement was observed in terms of dough sheet exit thicknesses and roll forces. The dataset highlight a simple relationship between roll forces and exit thickness providing definitions and measures for dough sheetability. The procedures for deriving parameters for the BB model for dough are described, and the importance of performing virtual sheeting tests for accurate estimation of dough elasticity and sheetability is highlighted. [1] Chakrabarti-Bell et al., (2010) J. Food Engr., (100) 278–288.

Prof. Yee-Kwong Leong (University of Western Australia)

The processing of mineral suspensions is employed in a range of unit operations in the mineral industry. The quality of this processing is significantly affected by their flow or rheological properties. Process optimization conditions determined by CFD modeling of suspensions in the processing vessels required an accurate knowledge of their rheological behaviour. Hence it is vital that rheological behaviour of suspension be characterised correctly. However there are pitfalls for inexperience and unsuspecting rheologists or technicians such as slip flows and shear banding at low shear rates. This talk will discuss the pitfalls and corrective steps to be taken for rheological characterization using a couette flow measuring geometry. If time permits I will discuss the range of surface forces that can be used to control the rheology of suspensions.

13 February 2013

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Monash University, Melbourne, Australia

Dr. Gregory Sheard (Monash University)

The flow of electrically conducting fluids, such as liquid metals, can be strongly modified when in the presence of magnetic fields. This talk will focus on a particular configuration of these general flows in which flow is through a rectangular duct, and the magnetic field is uniform and perpendicular to two of the duct walls and the flow, such as is found in the cooling blankets around magnetic confinement fusion reactors. Under these conditions, and assuming the duct walls are electrically insulated, the magnetic field acts to strongly suppress fluctuations in the direction of the magnetic field, rendering the flow almost two-dimensional when viewed in the direction of the magnetic field. An accurate quasi-two-dimensional model has been developed for this flow, with friction from the out-of-plane duct walls being described by adding a linear friction term to the two-dimensional Navier-Stokes equations. While being convenient from a modeling perspective, the damping in this magnetohydrodynamic flow suppresses the very flow fluctuations that promote mixing and heat transfer. In this talk, avenues for improving heat transfer under these conditions are explored arising from a study of the stability of linearized perturbations to the flow.

Dr. Guy Metcalfe (CSIRO)

Where do particles go? A Dynamical Systems perspective on the fate of inertial particles in laminar fluid flows

Material properties are significantly determined by the spatial distribution of particles in a fluid during processing. Foods, polymers and mineral slurries are several technological examples. Most of these particles are of such a size or density that the particle’s inertia is non-negligible, in other words the particle does not exactly follow fluid motion. One might expect in laminar flows, where viscous forces are relatively high, that particles might more readily follow fluid streamlines. Indeed in the commonly accepted theoretical picture inertial particles that deviate from a streamline exponentially reacquire a fluid streamline with a time-scale given by the particle’s Stokes number. However, recent theory that treats the particle motion as a dynamical system with augmented degrees of freedom predicts repellor regions in the flow that trigger large deviations of particle pathways from fluid pathways. To experimentally investigate these effects, our group has set up a laminar chaotic flow in a stirred tank where we have found a particle clustering instability. Particles initially distributed throughout the tank can spontaneously cluster into a KAM tube, a small region of the flow with helical fluid orbits that is separated from the larger region of chaotic orbits. Extension of theory to account for the strain field of the tank produces a clustering criterion that well agrees with the experimental data. This kinematics of clustering may lead to new flow designs that permit better control of particle location during processing.

25 January 2013

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RMIT University, Melbourne, Australia

Dr. Jean-Christophe Baudez (Irstea, UR TSCF, France)

In the current economical and environmental context, biosolids management is of major concern. Specific attention is particularly paid to rheological measurements which are presented as of special interest for mixing, chemical conditioning or dewatering. However, sewage sludge is often seen as a complex mixture and its rheological behaviour is considered to be highly dependent on the implemented treatments and on its composition. Thus, engineers need reliable data to model their process and research is focusing on parameters to evaluate physical consistency and rheological characteristics. On a practical point of view, because sewage sludge can be regarded as soft matter, improving knowledge on water/solid matter interactions is one of the clues to improve sludge rheology. In that purpose, this work focuses on the characterization of the water/solid matter interactions, based on water activity determination. These results are then related to sludge rheological properties, in order to check whether water activity can be representative of the evolution of sludge structure. Water activity is determined thanks to relative humidity measurements whereas oscillatory tests are performed to define sludge rheological behaviour. The impact of flocculation, solid content and ageing time on water activity and rheological parameters is studied. In accordance with the literature, in the range of considered solid contents, sewage sludge shows viscoelastic behaviour and the impact of flocculation is clearly highlighted. For raw sludge, both elastic and viscous moduli increase with the solid content whereas water activity decreases: the link between rheological characteristics can be modelled with two linear relationships, underlying a change between diluted and concentrated pastes. Similar tendencies are obtained with flocculated sludge. Polymer addition basically increases the values of elastic and viscous moduli and tends to slightly increase water activity values (for a given solid content), indicating water is becoming more accessible. The evolution of water activity and rheological properties with the ageing time is also shown, indicating that the change of sludge composition impacts water mobility.

24 October 2012

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Swinburne University, Melbourne, Australia

Dr. Sergey Suslov (Swinburne University of Technology)

Thermomagnetic convection and open questions in rheology of ferrocolloids ()

Nonuniform heating of a ferro-magnetic colloid placed into an external magnetic field results in a non-uniform magnetization of thefluid and, subsequently, in the appearance of a ponderomotive (Kelvin) force driving a stronger magnetized fluid toward regions with a stronger field. When combined with buoyancy the magnetic force leads to a rich variety of flow patterns that depend on the mutual orientation of forces and the temperature gradient. In this talk we will use flow stability and perturbation energy considerations to pinpoint physical mechanisms driving a fluid motion. Open questions arising from the current insufficient knowledge of the fluid's rheology will subsequently be discussed.

Assoc. Prof. Richard Manasseh (Swinburne University of Technology)

Fluid flows driven by sound and their applications ()

Sound is a wave phenomenon: according to linear theory, it simply causes molecules in a fluid to oscillate to and fro. However, non-linearity can cause sound (or ultrasound) to drive a continuous fluid flow, and can also cause fluid particles to migrate relative to a fluid. These effects occur either at high power (acoustic streaming), or at low power when there is a small discontinuity in the fluid owing to the presence of a meniscus, particle or bubble (microstreaming). The first quantitative experiments on microstreaming flows are presented, revealing a rich variety of fluid-flow patterns. Microstreaming can be applied to mixing, otherwise difficult to achieve owing to the absence of turbulence at microscale, and has now been developed for a specialised RNA test. Microstreaming is also implicated in the sonoporation phenomenon. Here, ultrasound stimulates cells to take in drugs or genes that would normally never enter cells, and stimulates stem cells to multiply. Surfactants are shown to have a significant effect on microstreaming behaviour.

12 July 2012

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University of Melbourne, Melbourne, Australia

Dr. Phillip Fawell (CSIRO)

Flocculant dilution effects on flocculation in mineral processing ()

The study of flocculation in mineral processing is complicated by the viscous nature of the aqueous solutions formed from high molecular weight acrylamide/acrylate copolymer flocculants. Comparisons of flocculant products suffer when physical mixing issues aren’t separated from “chemistry issues” associated with surfaces, adsorption and aggregate growth. In full-scale applications, excessively high flocculant concentrations can contribute to poor flocculation even in turbulent feedwells. This presentation will describe some results from a range of techniques that have been applied to better understand this problem, towards capturing such effects in computational fluid dynamics modelling.

Dr. Shane Usher (The University of Melbourne)

Yielding of coarse–fine particle mixtures in mineral slurries ()

The presence of coarse particulate components in tailings streams poses significant challenges to the mineral processing industry. The measurement of rheological and dewatering properties is critical to the design and operation of mixing, dewatering, pumping and tailings equipment and operations. However, the presence of coarse fractions can compromise the accuracy of traditional measurements.A methodology for predicting the gel point, close packing fraction and shear rheology of particulate slurries containing a binary mixture of fine and coarse material has been developed. The model has validity subject to the constraint that the particle size of the coarse material is sufficiently distinct from that of the fine material. The model enables calculation of the gel point and close packing fraction of the mixture based on the gel points and close packing fractions of the pure fine and coarse materials in the suspension. The model predicts that the gel point (and close packing fraction) of the fine material increases with increasing coarse fraction until a maximum value is attained before decreasing to the gel point (or close packing fraction) of the coarse material. This relationship provides a subsequent basis for a yield stress model to accurately predict the yielding behaviour of binary mixtures of fine and coarse material in both shear and compression. The model is useful in determining whether a sample exhibits yield stress behaviour through knowledge of the gel point and close packing fraction of the constitutive fine and coarse components. The model is exemplified using particulate mixtures containing coagulated aluminium oxide, calcium carbonate and coarse sand.

24 January 2012

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RMIT University, Melbourne, Australia

Prof. Gareth H. McKinley (MIT, USA)

Rheological fingerprinting of complex fluids and soft solids ()

Viscoelastic materials, such as many biomaterials and non-Newtonian fluids, typically experience mechanical loading which evokes a nonlinear rheological response. Such complex materials can provide novel functionality in biological and engineered systems. However, standard rheological characterization techniques are often insufficient to appropriately describe nonlinear viscoelasticity. We introduce a complete, low-dimensional language and framework (or ontology) for characterizing nonlinear viscoelasticity using large amplitude oscillatory shearing (LAOS) deformations. For many material systems the common practice of reporting only “viscoelastic moduli” as calculated by commercial rheometers (typically the first harmonic Fourier coefficients) is insufficient and/or misleading in describing nonlinear material phenomena. The mathematical structure of the nonlinear response is fully captured by higher Fourier harmonics, but these coefficients lack a clear physical interpretation. We build on the earlier geometrical interpretation of Cho et al. (2005) that decomposes a nonlinear stress response into elastic and viscous stress contributions using symmetry arguments. We then use Chebyshev polynomials as orthonormal basis functions to further decompose these stresses into harmonic components having physical interpretations. This framework naturally generates alternative measures of viscoelastic moduli, all of which reduce to G' & G" in the linear regime, but offer different physical insight into the nonlinear response. The results can be represented in the 2D space of frequency and strain-amplitude first discussed by Pipkin and generate a unique ‘rheological fingerprint’ of a viscoelastic material. We use this Chebyshev decomposition to propose physically meaningful material measures and clearly-defined concepts such as strain-stiffening/softening and shear-thickening/thinning which can be used in conjunction with graphical representations of the strain, strain-rate, and stress as the coordinate axes (‘Lissajous-Bowditch’ curves). The new ontology and associated software package (MITlaos) is general enough to be applied to any viscoelastic material, ranging from purely elastic to purely viscous. In general, LAOS fingerprinting is invaluable for both quantifying and describing the nonlinear rheological response of a wide range of materials including biopolymer gels, regenerative polymer networks, entangled melts and micellar solutions as well as extracting model parameters for nonlinear constitutive models. To illustrate the approach we examine the nonlinear rheological response of various soft materials including pedal mucus gel from terrestrial gastropods, wormlike micelle solutions, hydrogels and emulsion-based oilfield drilling fluid. These latter examples motivate our ongoing work on extending this ontology to quantitative description of elasto-visco-plastic materials and yielding transitions via large amplitude controlled stress deformations.

30 November 2011

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CSIRO, Melbourne, Australia

Dr. Ofer Manor (Monash University)

Challenges in microfluidics have initiated a renewed interest in surface acoustic waves (SAW) and in particular Rayleigh SAW for generating high fluid velocities and mixing in microchannels. SAW are generated by piezoelectric actuators that transfer electric to kinetic energy and give rise to different types of flow regimes — the Eckart and Rayleigh streaming and the Schlichting boundary layer. Here we extend the theory for the Schlichting boundary layer. We show that due to the complex nature of the Rayleigh SAW the leading order result for the steady flow in the Schlichting boundary layer is of greater magnitude than under the classic excitation of stationary planar waves. We confirm this result with two experimental studies. In the first study we measure the behaviour of a dilute suspension of 1 and 5 μm particles in 80 μm thick PDMS channels. In the second study we measure the spreading of thin liquid films. In both studies we use Rayleigh SAW as the excitation. In the first study we observe that a stationary planar acoustic wave results in a weak accumulation of particles on acoustic nodal lines due to the flow in the boundary layer. However, these structures are easily interrupted. In the presence of Rayleigh SAW, particle structures are found to maintain much better stability and to occupy a much larger area under dispersive flow effects. In the second study we elucidate the discrepancy between the displacement of drops and the spreading of films. Drops displace in the propagation direction of the surface wave while thin liquid films spread in both directions. The reason for this behaviour is found in the Schlichting boundary layer.

Dr. Andrew Chryss (CSIRO)

Settling of particles in sheared flows

The pipeline transport of highly concentrated suspensions of mineral ores and tailings results in laminar flow of coarse, multi-phase, non-Newtonian suspensions. The settling of particles that occurs under these circumstances is an operational difficulty for operators of long pipelines. As a first stage to the modelling of the processes involved, the study of settling in sheared flows has been undertaken by several workers with some limited success. A presentation of earlier work conducted by CSIRO and RMIT will form the basis for a discussion of the issues involved.